Polarization is the process in which spherical circulating lymphocytes shift to a motile, tissue-invasive form. The polarization process is a potential target for therapeutic manipulation of lymphocyte traffic. One type of signal known to trigger and maintain T cell polarization is the engagement of integrin receptors by ECM components. We will elucidate the mechanisms of two essential and interrelated features of integrin-mediated human T cell polarization, the determination of anterior-posterior polarity, and the development of Iocomotory appendages. Engagement of the alpha 2 beta 1 receptor will be the main polarization stimulus. Polarization results in the development of an anterior pole bearing multiple motile lamellipodia, which generate tractive force; and a posterior pole bearing a single, snout-like, highly adhesive uropod, which provides posterior anchorage. We have found that these poles do not interchange but remain constant during prolonged periods of migration and directional change. We have also found that the posterior pole invariably develops at the site of the microtubule organizing center (MTOC), an assembly of tubulins, microtubule-associated proteins, and signal transducers. This indicates that the MTOC either acts as an organizing center for structural and signaling proteins which regulate uropod development, or that the MTOC is recruited to such a center before the uropod becomes evident. In either case, the MTOC is a useful marker for studying the differentiation of the posterior T cell pole. The first aim of the project is to characterize the MTOC and adjacent cytoskeleton in order to determine how their composition and structure change with polarization. Both immunocytochemical and ultrastructural approaches will be taken. The second aim is to test the hypothesis that members of the Rho family of GTPases are regulators mediators of integrin- induced T cell polarization and appendage formation. Rho-family GTPases are known to perform this function in many nonlymphoid cell types, but their role in the ECM-induced polarization and migration of T cells has not been examined. We will determine the effects of constitutively active and dominant negative mutant GTPases on integrin-induced appendage formation, adhesion, and motility.